1. Field of the Invention
Exemplary aspects of the present invention relate to a development device, and more particularly to a development device using a two-component developer. In addition, the exemplary aspects of the present invention also relate to an image forming apparatus and a process cartridge using a development device.
2. Description of the Related Art
A related art development device, which employs a two-component developer including a toner and a magnetic carrier, for use in an image forming apparatus includes a supply conveyance path and an agitation conveyance path to circulate the developer. The supply conveyance path supplies the developer to a developer carrying member while conveying the developer to a direction parallel to the axis of an image carrying member. The agitation conveyance path conveys the developer in a direction opposite to the supply conveyance path while agitating the developer.
In a such development device, the developer thus supplied to the developer carrying member passes a development region, and is collected in the supply conveyance path. The toner in the developer is consumed in the development region and, the developer is mixed with the developer within the supply conveyance path. The more developer located on the downstream portion of the supply conveyance path, the greater the amount of developer particles passing through the development region. Consequently, the more developer located downstream of the supply conveyance path in a developer conveyance direction, the lower the toner density the developer has. When the toner density decreases, the image density of an image developed by the developer decreases. In other words, the image density of an image varies at the upstream side and downstream side in the developer conveyance direction of the conveyance path in which the developer is supplied to the developer carrying member, resulting in generation of an uneven density image.
In addition, the developer used for development is collected through the agitation conveyance path. The developer reaching the end of the downstream side of the agitation conveyance path in the developer conveyance direction is transferred to the end of the upstream side of the supply conveyance path in the developer conveyance direction. The developer collected at a position closer to the downstream side of the agitation path in the developer conveyance direction is agitated for a shorter time period. Accordingly, the developer collected at the downstream side of the developer conveyance direction of the agitation conveyance path is immediately supplied to the supply conveyance path. This immediate supply of the collected developer causes inadequate agitation of the developer, resulting in non-uniform charging of the toner, thereby decreasing of the image density even if the toner density is maintained at an appropriate level.
One example attempts to reduce the deterioration of the toner density and image density by providing an additional conveyance path serving as a collection conveyance path in a development device. Specifically, the development device as well as the collection conveyance path include a supply conveyance path and an agitation conveyance path. The supply conveyance path is disposed at substantially the same level as that of the developer carrying member to convey and supply the developer to the developer carrying member. The collection conveyance path is disposed below the developer carrying member to collect and convey the collected developer. The agitation conveyance path is disposed at substantially the same level as that of the collection conveyance path and below the supply conveyance path. The agitation conveyance path agitates excess developer reaching the end of the downstream side of the supply conveyance path relative to the developer conveyance direction, and the collected developer reaching the end of the downstream side of the collection conveyance path relative to the developer conveyance direction. The supply conveyance path, collection conveyance path and agitation conveyance path are disposed to be parallel to the developer carrying member. The conveyance paths are separated from one another by separation members. One separation member is disposed between the end of the downstream side of the agitation conveyance path and the supply conveyance path, and includes an opening so that the agitated developer is transferred to the supply conveyance path through the opening. Another separation member is disposed between the end of the downstream side of the supply conveyance path and the agitation conveyance path, and includes an opening so that the excess developer is transferred to the agitation conveyance path through the opening. Still another separation member is disposed between the end of the downstream side of the collection conveyance path and the agitation path, and includes an opening so that the collected developer is transferred to the agitation conveyance path through the opening. By providing an additional collection conveyance path, the developer can be supplied and collected independently.
The collection conveyance path is disposed below the developer carrying member in such a manner that the collected developer in the collection conveyance path is adhered to the developer carrying member when the volume of the collected developer in the collection conveyance path reaches a certain level. The collection conveyance path conveys the collected developer from the upstream side to the downstream side thereof, and transfers the developer from the downstream side thereof to the agitation conveyance path. In the course of the transfer from the downstream side of the collection conveyance path to the agitation conveyance path, the developer conveyance direction of the collected developer shifts significantly. Consequently, the collected developer can be accumulated at the downstream side of the collection conveyance path, and the height of the collected developer can reach higher than a certain level. In this case, the collected developer in the collection conveyance path is re-supplied to the developer carrying member, resulting in an occurrence of a problem in that the collected developer having an inappropriate toner density (i.e., the toner is consumed) is mixed with the developer having an appropriate toner density. Thereby, the toner density can be decreased, and uneven images can be generated.